Fog + Ice = AC


As part of today’s show, someone called in with a subaru that had the AC “freezing”. It started by “fog” coming through the vents. This, according to the caller, was followed by the AC not working. When they stopped and popped the hood, they found ice. The dealer told them it had to do with air intake.

I bought a new Mazda Protege in 2001 and have experienced this identical phenomenon. It starts with “fog” which is warm, humid air blowing into a cool car. At first we found water on the floor, but found that something on the passenger side under the dash was covered in ice. I took it to two Mazda dealership and they basically said I was nuts. The only remedy is to “defrost” the system by turning off the AC for about 5 minutes to melt both the system and driver. The only other pattern I have noticed in the last 6 years is that the more humid it is outside, say a dewpoint of 70 versus 60, the quicker the AC freezes. The car now has 100,000 miles on it with the same problem. Any ideas?


It’s not a rare problem. The evaporator is freezing up due to one of several possible causes. Slight refrigerant loss leading to abnormally low pressures on the low side, failed cycling switch or expansion valve, etc.

The first step should be to put the gauges on the car and see what’s going on with the pressures.


It is not all that unusual. It is exactly what you suggest. Usually it is an indication that there is a pressure issue. A good A/C shop should be able to check it out for you.

Some systems are just prone to it. It will only happen under certain weather conditions as you are aware and all you need do is to turn it off and let the ice melt.


Icing on the evaporator is not uncommon, and it does indicate a repairable fault with your A/C system. As others have said, the two Mazda dealerships don’t know what they’re talking about.

Find yourself a good automotive A/C specialist. You’ll be told “Happens all the time. We had two last week. Leave it with us now, pick up tomorrow.” Good luck.


The compressor should cycle off before freezing up on either a pressure switch, and or evaporator temperature sensor depending on the vehicle. one of these is malfunctioning


Ignore Star’s advice. He is the resident, non-expert on automotive A/C and everything he stated is total BS.
As usual. A troll or comedian; it’s still undecided.


Thanks for the suggestions. One dealership took it for a day and couldn’t locate the problem. Of course, these clowns brought the wrong car out when I came to pick it up. I’ll mention your comments to my local mechanic next time I’m at the shop.